The deprotonative metalation of [1,2,3]triazolo[1,5-a]quinoline. Synthesis of 8-haloquinolin-2-carboxaldehydes

New highly functionalized triazoloquinolines were synthesized by applying polar organometallic methods. Double metalation and functionalization provided 3,9-dihalogenated triazoloquinolines. Ring opening of the triazole with loss of nitrogen has been performed for the first time with 3,9-dihalogenated triazoloquinolines allowing the access toward 8-haloquinolin-2-carboxaldehydes under oxidant-free conditions. This approach demonstrates that the triazole ring can be used as protecting group of 2-quinolinecarboxaldehydes, activating the C9-position for lithiation and functionalization by triazole ring opening. 8-Haloquinoline-2-carbaldehydes become in this way readily available. (C) 2009 Elsevier Ltd. All rights reserved.